Rissanen Antti Juhani, Mangayil Rahul, Tveit Alexander T, Maanoja Susanna T, Khanongnuch Ramita
Faculty of Engineering and Natural Sciences, Tampere University, Tampere, Pirkanmaa, Finland.
Natural Resources Institute Finland, Helsinki, Uusimaa, Finland.
Microbiol Spectr. 2025 Jul;13(7):e0313324. doi: 10.1128/spectrum.03133-24. Epub 2025 Jun 9.
Gammaproteobacterial methanotrophic bacteria (gMOB) are dominant methanotrophs in the water column of oxygen-stratified boreal and subarctic lakes and ponds. (Meta)genomic data suggest that, besides methane (CH), gMOB potentially use dissolved organic matter (DOM) and reduced sulfur compounds (e.g., sulfide) as electron sources. To study the DOM and sulfide metabolism of lake gMOB, we subjected a psychrophilic lake water strain, sp. S3L5C, first to different sulfide levels (NaS, 0-5 mM) to test the toxicity, and subsequently, to freshwater DOM (60 mg L) either alone or with sulfide (0.05 mM) at 1 and 20% CH levels. The growth, CH and O consumption, CO production, and mRNA expression patterns of S3L5C were analyzed. Sulfide concentrations of 0-0.5 mM had no effect, while 1 and 5 mM concentrations inhibited the strain's growth. At 20% CH, DOM addition enhanced CH consumption, CO production, and growth of S3L5C, while the addition of sulfide+DOM led to further increases in these variables. The addition of sulfide+DOM enhanced CH consumption even at 1% CH. The effect of DOM on the S3L5C's metabolism was accompanied by enhanced expression of the gene, which has been suggested to mediate the extracellular electron transfer from DOM. Furthermore, the addition of sulfide+DOM enhanced the expression of the and genes encoding dissimilatory sulfide and thiosulfate oxidation, respectively. Together with previous metagenomic data, these results suggest that the usage of DOM and reduced sulfur compounds as electron sources is a trait that enhances methanotrophy among gMOB of boreal and subarctic lakes and ponds.IMPORTANCEGammaproteobacterial methanotrophic bacteria (gMOB) are crucial mitigators of methane emissions of many ecosystems, like boreal and subarctic lakes and ponds. Metagenomic data suggest that besides using methane, gMOB have genetic potential to use dissolved organic matter (DOM) and sulfide, typically present in lakes and ponds, as electron donors. To test the effect of DOM and sulfide on the methane metabolism of gMOB of oxygen-stratified boreal lakes, we subjected our recently isolated lake gMOB strain, sp. S3L5C, to additions of freshwater DOM and sulfide. We show that DOM and sulfide enhance methane consumption and growth of S3L5C. Furthermore, the expression of genes mediating the electron transfer from DOM and sulfide is enhanced. Our results suggest that the usage of DOM and reduced sulfur compounds as electron sources is a trait that enhances methanotrophy among gMOB and adds significantly to the growing body of literature highlighting the enormous metabolic versatility of gMOB.
γ-变形菌纲甲烷营养细菌（gMOB）是氧气分层的北方和亚北极湖泊及池塘水柱中的主要甲烷营养菌。（宏）基因组数据表明，除了甲烷（CH₄），gMOB还可能利用溶解有机物（DOM）和还原态硫化合物（如硫化物）作为电子源。为了研究湖泊gMOB的DOM和硫化物代谢，我们将一株嗜冷湖水菌株，sp. S3L5C，首先置于不同硫化物水平（Na₂S，0 - 5 mM）下以测试其毒性，随后，在1%和20% CH₄水平下，使其单独接触淡水DOM（60 mg/L）或与硫化物（0.05 mM）一起接触。分析了S3L5C的生长、CH₄和O₂消耗、CO₂产生以及mRNA表达模式。0 - 0.5 mM的硫化物浓度没有影响，而1 mM和5 mM的浓度抑制了该菌株的生长。在20% CH₄条件下，添加DOM增强了S3L5C的CH₄消耗、CO₂产生和生长，而添加硫化物 + DOM导致这些变量进一步增加。即使在1% CH₄时，添加硫化物 + DOM也增强了CH₄消耗。DOM对S3L5C代谢的影响伴随着该基因表达的增强，该基因被认为介导了从DOM的细胞外电子转移。此外，添加硫化物 + DOM增强了分别编码异化硫化物和硫代硫酸盐氧化的基因和的表达。与先前的宏基因组数据一起，这些结果表明，利用DOM和还原态硫化合物作为电子源是一种增强北方和亚北极湖泊及池塘gMOB中甲烷营养作用的特性。
重要性
γ-变形菌纲甲烷营养细菌（gMOB）是许多生态系统（如北方和亚北极湖泊及池塘）甲烷排放的关键缓解者。宏基因组数据表明，除了利用甲烷，gMOB具有利用湖泊和池塘中通常存在的溶解有机物（DOM）和硫化物作为电子供体的遗传潜力。为了测试DOM和硫化物对氧气分层的北方湖泊gMOB甲烷代谢的影响，我们将我们最近分离的湖泊gMOB菌株，sp. S3L5C，置于添加淡水DOM和硫化物的环境中。我们表明DOM和硫化物增强了S3L5C的甲烷消耗和生长。此外，介导从DOM和硫化物进行电子转移的基因表达增强。我们的结果表明，利用DOM和还原态硫化合物作为电子源是一种增强gMOB中甲烷营养作用的特性，并显著增加了越来越多强调gMOB巨大代谢多功能性的文献。
